Burner control system using a radiation operated relay means

ABSTRACT

A SUBSTANTIALLY ALL SOLID STATE CONTROL SYSTEM WHICH IS ADAPTED TO BE CONNECTED TO CONTROL A FUEL BURNER IS DISCLOSED AND PROVIDES A DELAYED FUEL AND POST-IGNITION TIMING PERIOD USING A HEATER OPERATED BIMETAL SWITCH. THE SYSTEM IS ADAPTED TO BE ENERGIZED THROUGH A LINE VOLTAGE THERMOSTAT TO PROVIDE POWER TO A FUEL BURNER MEANS WHICH MAY INCLUDE TWO STAGES OF FUEL CONTROL, ALONG WITH AN IGNITION MEANS AND FLAME DETECTION MEANS. THE SYSTEM INCLUDES A MAIN CIRCUIT MEANS HAVING TRIACS FOR CONTROL, AND FOR OPERATION OF THE VALVES THAT SUPPLY FUEL TO THE FUEL BURNER MEANS. THE SWITCHING BETWEEN THE TRIAC STAGES IS ACCOMPLISHED BY A RADIATION OPERATED RELAY MEANS WHICH INCLUDES TWO RADIATION SOURCES AND A RADIATION RESPONSIVE MEANS. THE RADIATION OPERATED RELAY MEANS PROVIDES A SOLID STATE SUBSTITUTION FOR A MORE CONVENTIONAL TYPE OF RELAY.

R. L. HRON June 27, 1972 BURNER CONTROL SYSTEM USING A RADIATION OPERATED RELAY MEANS Filed March 15, 1971 I N VENTOR ROLAND L. HRON A TTORIVEX United States Patent 3,672,811 BURNER CONTROL SYSTEM USING A RADIATION OPERATED RELAY MEANS Roland L. Hron, Bloomington, Minn., assignor to Honeywell Inc., Minneapolis, Minn. Filed Mar. 15, 1971, Ser. No. 124,128 Int. Cl. F23n 5/00 U.S. Cl. 431-69 9 Claims ABSTRACT OF THE DISCLOSURE A substantially all solid state control system which is adapted to be connected to control a fuel burner is disclosed and provides a delayed fuel and post-ignition timing period using a heater operated bimetal switch. The system is adapted to be energized through a line voltage thermostat to provide power to a fuel burner means which may include two stages of fuel control, along with an ignition means and flame detection means. The system includes a main circuit means having triacs for control, and for operation of the valves that supply fuel to the fuel burner means. The switching between the triac stages is accomplished by a radiation operated relay means which includes two radiation sources and a radiation responsive means. The radiation operated relay means provides a solid state substitution for a more conventional type of relay.

CROSS REFERENCE TO RELATED APPLICATIONS The present application relates to a U.S. patent application S.N. 124,129, filed on even date with the present application, directed to a delayed fuel and post ignition timed burner control system disclosed but not claimed in the present application. The related application is filed in the name of Roland L. Hron et a1. and is assigned to the assignee of the present invention.

BACKGROUND OF THE INVENTION In the operation of fuel burner means, safety and reliability are essential, One normally used component or device in most burner control systems is a conventional electromagnetically operated relay. This type of relay has had the inherent problem of all mechanical devices, that is, it is a device that is subject to mechanical wear. Electromagnetic relays in burner control systems, that otherwise are substantially made of solid state components, may create an undesirable condition and safety hazard. It is therefore desirable to eliminate as many electromechanical relays and components as possible.

SUMMARY OF THE INVENTION The present invention is directed to a fuel burner control system that is adapted to be connected to a fuel burner means, and a condition sensing means or thermostat, and which is capable of reliable operation through the use of solid state components. A photoelectric type of relay, or radiation operated relay means including two radiation sources and a radiation responsive means, are used to provide a relaying function in the present invention. The radiation operated relay means is made up of an incandescent light bulb, a neon voltage regulating tube, and a cadmium sulfide type of photocell. The incandescent light bulb is energized to change the impedance of the photocell which is in turn used to trigger a solid state switch into conduction which energizes a voltage breakdown tube. The light generated by the voltage breakdown tube also falls on the photocell and in effect latches the system much as a latching relay would operate.

3,672,811 Patented June 27, 1972 BRIEF DESCRIPTION OF THE DRAWING The single figure of the present application is a complete schematic diagram of a burner control system connected to a fuel burner means, a temperature sensing means or thermostat, through conventional limit switch and a safety switch.

DESCRIPTION OF THE PREFERRED EMBODIMENT A conductor 10 and terminal 19 at conductor 11 are connected to a conventional source of alternating current voltage for energizing the fuel burner control system generally disclosed at 12 and which is adapted to be connected to a fuel burner means 13. Conductor 10 is connected through a limit control 14, such as a boiler low water out out or temperature responsive switch, as is well-known in the art. The limit 14 is in turn connected to terminal 15, a fuse 16, and a normally closed safety switch contact 17 that is thermally linked at 20 to a safety switch heater 21 within the fuel burner control system 12. The safety switch heater 21 and the safety switch 17 are of a conventional design wherein the heater 21 opens the contact 17 in the event of an unsafe condition and normally is reset manually. Safety switch 17 is in turn connected to a terminal 22 that connects through a condition sensing means 23 (shown as a conventional thermostat) to a further terminal 24. When the condition sensing means or thermostat 23 is closed, power is supplied to the fuel burner control system 12 and the fuel burner means 13.

The fuel burner means 13 a number of terminals 25, 26, 27, 28, 30 and 31 which allow the fuel burner means 13 to be connected to the fuel burner control system 12. Terminal 25 is connected to the terminal 24 by conductor 32 and supplies energy to a fan 33 that is also connected to terminal 30 which in turn is connected to conductor 11 to supply alternating current to the fan 33 as soon as the thermostat 23 closes.

A two-stage fuel burner 34 is disclosed having two valves 35 and 36 which supply fuel to the burner 34 from a common supply source 37, The valve 35 has associated with it a solenoid actuator 38, while the valve 36 has a solenoid actuator 39. Valve actuator 39 can be placed in parallel with fan 33 across terminals 27 and 30 for a pre-ignition hookup. The solenoid actuators and valves are of conventional design and admit fuel to the burner 34 by the solenoid 39 first becoming energized thereby opening valve 36, and the subsequent opening of valve 35 by the energization of the solenoid 38. Also included in the fuel burner means 13 is a spark ignition transformer 40 having a spark gap 41 for ignition of fuel from the burner 34. The transformer 40 has a primary winding 42 that is connected between the terminals 28 and 30 of the fuel burner means 13.

To complete the fuel burner means 13, a flame sensing device or photocell 43 is provided, and the photocell 43 is connected between the terminals 31 and 30 of the fuel burner means 13. The photocell 43 has a relatively high resistance when no flame exists at the burner 34, and has a very low resistance when a flame is present at the burner 34. The photocell is of a conventional design. The photocell can be replaced by any type of flame sensing device which would provide two levels of output depending on whether a flame exists or does not exist at the burner 34.

The terminals 9, 15, 22 and 24 provide input terminals for the fuel burner control system and are adapted for easy connection to conventional equipment. Terminals 25 through 31 provide means to adapt the connection of the fuel burner control system 12 to a fuel burner means 13, and all of the equipment in the fuel burner means 13 and connected to the input terminals are conventional in nature 3 and do not form part of the present invention. The invention is in the fuel burner control system 12 which is adapted to be connected to the terminals set forth above.

In the fuel burner control system 12, a main supply conductor 45 is provided which connects to terminal 24 and provides energy to a bias means made up of conductor 46, resistor 47, and capacitor 48. The bias circuit means has a junction point 50 that is connected by conductor 51 to terminal 31 and thereby to the photocell 43. The point 50 is also connected through a diac or voltage breakdown device 52 to a gate 53 of a triac Q1. The triac Q1 is connected by conductor 54 to a conductor 55 that joins the terminals 9 and 30 to supply one side of the line 11 to the fuel burner means 13. The other side of the triac Q1 is connected by conductor 56 to a common point 57, a conductor 58 and timer heater 60, which forms part of a time switch means 61. The time switch means 61 includes a double throw switch having terminals 62, 63, and a common terminal 64 that is in turn connected at 65 to conductor 45. The time switch means 61 includes in its structure a bimetal 59 which is responsive to the timer heater 60 to position the double throw switch between the position shown with terminals 63 and 64 connected for a delayed fuel period when the timer heater 60 is cold. The switch means 61 would be closed between terminals 64 and 62 for a post-ignition timing function when the timer heater 60 is sufiiciently hot to warp the bimetal 59 to operate the switch mechanism.

The switch terminal 62 for post-ignition is connected by a conductor 66 through a diode 67 to the previously mentioned safety switch heater 21. This forms part of a main circuit means for the triac Q1. The safety switch heater 21 in turn is connected to a radiation operated latching relay means 70 of a rather unusual nature. The relay means 70 includes an incandescent light bulb 71 that is connected between the safety switch heater 21 and the junction 57 in series circuit with the triac Q1. Radiation emitted from the light bulb 71 falls on a radiation responsive means or photoresistor 72, such as a cadmium sulfide photocell, that is also subject to radiation from a neon voltage breakdown type bulb 73 that forms part of the relay means 70. The neon bulb 73 is connected at a common point 74 to the terminal 27. The other side of the neon bulb 73 is connected by conductor 75 through a resistor 76 to conductor 55. The operation of the neon bulb 73 and the relay means 70 will be described in detail in the subsequent specification. The common point 74 is connected by conductor 80 through a triac Q3 and conductor 81 to the conductor 45 for a supply of power to the neon bulb 73 and to the terminal 27 when the triac Q3 is in conduction. A gate 83 of the triac Q3 is connected by conductor 84 to the photoresponsive impedance 72.

To complete this portion of the circuit, a diode 85 is connected between the condctor 80 and the diode 67 at the point where it joins the safety switch heater 21. The diode 85 provides a unique protective function to provide a fail-safe mode of operation in the event that the triac Q3 should become short circuited and this function will be described in connection with the operation of the overall system. It also provides a current path for the safety switch 21 in case of flame failure after the control has gone through its normal startup and the timer switch means 61 has returned to the cold (delayed fuel) position. Flame failure will cause the safety switch 21 to start heating immediately.

The burner control system 12 has a capacitor 86 and resistor 87 between the junction 57 and a gate 90 of a triac Q2. A triac Q2 is connected by conductor 91 to conductor 45 and by conductor 92 to terminal 28 of the fuel burner means 13. To provide for a post-ignition function and to complete the described circuitry, a diode 93 is connected between the switch terminal 62 and the terminal 28 of the fuel burner means 13 to provide for half wave energization of the transformer 40 in the fuel burner 4 means 13 during a portion of the operating cycle of the control system.

OPERATION With an alternating current potential on conductors 10 and 11 and the thermostat 23 open, the system is in a standby condition awaiting normal operation. The closing of the thermostat 23 applies power on conductor 32 directly to the fan 33 to start the fan into operation. At this same time energy is supplied to the main circuit means and the bias circuit means to provide a voltage at point 50 to trigger the triac Q1 into conduction. The triac Q1 conducts through the time switch means 61 by conducting through conductor 65 and the timer heater 60 (in the position shown in the drawing). This operation provides a triggering pulse from the junction 57 through the capacitor 86 and the resistor 87 to the gate of triac Q2 and causes the triac Q2 to be conductive through the pimary winding 42 of the transformer 40. The operation of triacs Q1 and Q2 simultaneously thereby starts a timing function by heating the timer heater 60, and starts a spark in the fuel burner means 13 across the spark gap 41.

The timer heater 60 operates for approximately 10 to 20 seconds before the heat generated is suflicient to cause the time switch means 61 to switch so that terminals 62 and 64 are connected by the time switch means 61. This immediately deenergizes the timer heater 60, but provides a current through the conductor 66 and the diode 67 along with the safety switch heater 21 to the bulb 71. Since the triac Q1 still has a bias supplied from the junction 50, it remains in conduction thereby drawing current through the bulb 71 lighting that bulb. This current flow starts the heating of the safety switch heater 21, as well as providing a radiation from the bulb 71 which is sensed by the photoresistor 72. The photoresistor 72 changes value to provide a trigger pulse for the triac Q3. This trigger pulse turns the triac Q3 on and current is then conducted through the neon bulb 73 along with a second path which includes the terminal 27 of the fuel burner means 13 and the solenoid 39 of the vvalve 26. The current flowing through the solenoid 39 opens the valve 36 and allows gas or oil to flow to the burner 34 for ignition by the spark being generated at the gap 41.-

The operation of the triac Q3 causes the neon tube 73 to generate a radiation which falls on the photoresistive resistor 72 to in effect latch the triac Q3 into conduction. This is accomplished by providing a photoresistor 72 which has a time constant longer than the pulses per second that flow through the neon tube 73 at 60 hertz. If the time constant of the resistor 72 is sufliciently long the pulses of light occurring at 120 cycles per second from the neon bulb appear to be a continuous light tlowing to the photoresistive element 72 thereby keeping the triac Q3 in conduction. The initial light or radiation being generated from the bulb 71 acts as a pull in for the solid state or photorelay means 70 while the light or radiation being generated by the conduction through the neon bulb 73 acts to latch this relay mechanism into operation. The relay means 70 therefore is a form of solid state relay that contains no contacts, and due to the selection of components has an exceedingly long and reliable life.

With the time switch means 61 in the position where terminals 64 and 62 are connected, the valve 36 is open and full wave energy is being supplied to the primary winding 42 of the spark transformer 40 so that a spark is generated. As soon as the spark ignites the fuel flowing from the burner 34, the photocell 43 senses the existence of flame and its impedance changes to a relatively low value. The photocell 43 is connected across the capacitor 48 in the bias circuit means for the triac Q1 and this relatively low value tends to short out the gate signal to the triac Q1 thereby turning the triac Q1 off. As soon as the triac Q1 is turned off no gating signal is available for triac Q2 and it also turns off. This also removes the flow of current through the bulb 71 but the solid state relay means 70 remains energized due to the light emitted by the neon tube 73. As soon as the triac Q1 turns off, there is no current flowing in the safety switch heater 21 thereby eliminating the possibility that the device will go out on safety as a flame has been sensed.

In order to provide a post-ignition timing function, a half wave circuit is provided through the diode 93 and through the primary winding 42 when the time switch means 61 is in the right hand position. This half wave energy provides an adequate spark to guarantee the continued ignition of the fuel from the burner 34.

After a cooling time interval for the timer heater 60, the time switch means 61 switches back to the left hand position, as shown in the drawing. The system does not start again as it did at the outset since the photocell 43 secs flame and effectively shorts out the gate signal to triac Q1. The switching of the time switch means 61 to the left position substantially removes a short circuit from the solenoid 38 of the second stage of fuel. The removal of this short circuit, in the form of the removal of the diode 93 from the circuit, allows the second stage of fuel to be energized by the solenoid 38 being energized to open rvalve 35 thereby increasing the fuel flow to the burner 34. The second stage disclosed is an auxiliary or additional feature and may or may not be used in certain forms of burner installations.

In the event of the short circuiting of any of the triacs Q1, Q2, or Q3, a safe failure mode is established in the present system. The shorting of the triac Q1 causes the system to become inoperative by the safety switch heater remaining in the system after the operation of the photocell detecting flame and therefore the system locks itself out on safety. The shorting of the triac Q2 provides a constant ignition spark at the burner and any admission of fuel to the burner would be ignited for proper operation. The only component which could have caused trouble upon shorting was disclosed as the triac Q3. The shorting of triac Q3 could have caused an unsafe mode of operation were it not for the diode 85. In the event that the triac Q3 short circuits, the current drawn by the diode 85 upon the operation of the triac Q1 causes current to flow through the safety switch heater 21 and would cause the system to shut down by the safety switch 17 opening. Also, in the event of flame failure when operating, the diode 85 provides a current path to heater 21 to cause safety switch 17 to open.

The present system discloses a substantially all solid state fuel burner control system that is adapted to be connected to a fuel burner means and wherein component failures cause a safe operating condition or a safety shut down that normally requires manual reset and therefore proper service attention before the system can be placed back into operation.

The embodiments of the invention in which an exclusive property or right is claimed are defined as follows:

1. A fuel burner control system adapted to be connected to fuel burner means having ignition means, fuel supply means, and flame sensing means, with said control system further adapted to respond to condition sensing means including: main circuit means including bias circuit means connected to operably energize first solid state switch means upon application of electrical power to said system by operation of said condition sensing means; said solid state switch means further connected to operactively energize safety switch timer means and adapted to energize said ignition means; radiation operated relay means including two radiation sources and radiation responsive means with a first of said radiation sources energized in circuit with said safety switch timer means to cause said radiation responsive means to change in impedance; and second solid state switch means operated by said change in impedance to energize a second of said radiation sources to maintain said change of impedance to thereby latch said relay means into an energized condition by conduction through said second solid state switch means; said second solid state switch means adapted to operate said fuel supply means to admit fuel to said fuel burner means; said flame sensing means adapted to be connected to said bias circuit means to change a bias to said first solid state switch means to deenergize said first solid state switch means and thereby deenergize said safety switch timer means and said first radiation source upon the advent of flame in said burner means.

2. A fuel burner control system as described in claim 1 wherein said first of said radiation sources is a light radiating source.

3. A fuel burner control system as described in claim 2 wherein said light radiation source is an incandescent type light bulb.

4. A fuel burner control system as described in claim 3 wherein said second of said radiation source is a gas discharge radiating source.

5. A fuel burner control system as described in claim 4 wherein said gas discharge radiating source is a neon voltage breakdown type of device.

6. A fuel burner control system as described in claim 1 wherein said radiation responsive means is a photoconductive type of variable resistance means.

7. A fuel burner control system as described in claim 6 wherein said resistance means is a cadmium sulfide type of photocell.

8. A fuel burner control system as described in claim 5 wherein said radiation responsive means is a photoconductive type of variable resistance means.

9. A fuel burner control system as described in claim 8 wherein said resistance means is a cadmium sulfide type photocell.

References Cited UNITED STATES PATENTS 3,317,789 5/1967 Nuckolls 307252 T 3,348,131 10/1967 Banks 307252 B 3,574,496 4/ 1971 =Hewitt 43 l79 CARROLL B. DORITY, J 11., Primary Examiner US. Cl. X.R. 

